Mill Scale Removal

I use phosphoric acid (sold as prep and etch). The problem with HCL is that it leaves behind chlorides on the metal, which promote corosion through chloride complexes with the iron. The phosphoric acid leaves a phospate coating, which tends to prevent corosion. I use the liquid for small parts that I can dip, for larger sections I use the gel stuff, if I don't care about he surface finish (for say, large structural steel with a crappy surface finish to begin with ) I use a needle scaler to break the oxide up before I use the acid. Good luck on your new welding endeavor, I really love TIG, but it can be a bit slower than other methods.
 
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